Method and apparatus for providing a hard metal coating on confined areas of a metal part

ABSTRACT

A metal part to be clad is conveyed past a plurality of treating stations arranged along a definite path. At the first station, the metal part has the surface on which the coating or cladding is to be applied machined to include a receiving groove. The part is then transported to the next station where a suitable hard cladding material in particulate form is deposited onto the specially machined area of the metal part. The part is then heated to where the temperature of the coating material is raised sufficiently to melt it, then the metal part is moved to a finishing station where the coating is machined to prescribed dimensions and surface condition.

United States Patent 1191 Hanson et al.

[ June 26, 1973 [75] Inventors: Charles A. Hanson; Leroy C. Cowles,

both of Long Beach, Calif.

[73] Assignee: Pacific Valves, Inc., Long Beach,

Calif.

22 Filed: Feb. 24, 1970 21 App1.No.: 13,674

Parikh et a1. 29/420.5

3,431,105 3/1969 Heck 29/420.5 X 3,479,258 11/1969 Ashcroft 29/527.2 X 2,129,702 9/1938 Merle 164/46 1,128,059 2/1915 Schoop 164/46 X 1,947,493 2/1934 Rose et a1. 164/46 X 2,864,137 12/1958 Brennan 164/46 2,998,322 8/1961 Strate 118/308 X Primary Examiner-Charles W. Lanham Assistant Examiner-D. C. Reiley, Ill Attorney-George J. Netter and Kendrick and Subkow [57] ABSTRACT A metal part to be clad is conveyed past a plurality of treating stations arranged along a definite path. At the first station, the metal part has the surface on which the coating or cladding is to be applied machined to include a receiving groove. The part is then transported to the next station where a suitable hard cladding material in particulate form is deposited onto the specially machined area of the metal part. The part is then heated to where the temperature of the coating material is raised sufficiently to melt it, then the metal part is moved to a finishing station where the coating is machined to prescribed dimensions and surface condition.

7 Claims, 9 Drawing Figures ssu e.-

PAIENIEDJUNZS ms 3. 740.833

sum 1 0F 5 07442455 W3 2? 462W 6. cam/465 A 7700M? V53 PAIENTEDJUHZB ms 3. 740.833

sum 5 or 5 INVEN ORI 65507 C. n 665 W A fg A g V5 1 METHOD AND APPARATUS FOR PROVIDING A HARD METAL COATING ON CONFINED AREAS OF A METAL PART BACKGROUND OF "THE INVENTION The present invention pertains generally to the production of hard coatings on metal parts, and, more particularly, to methodand apparatus for providing a hard alloy layer onto selected surface portions "of a metal body.

Not infrequently mechanism parts may be subjected, during use, to exceptionally great pressures, shock loading or abrasion as 'to require their being constructed of 'high strength materials orhave their active surfaces treated as to make them able to withstand the normal operating condition. For example, a valve seat may be subjected repeatedly'to seating pressure on closure which, unless the valve seat is made of a sufficient hard material, will rapidly deteriorate it in use, necessitating replacement or repair. If'such parts are made in their entirety from a suitably hard material, the cost may be prohibitively .high,and-therefore a more practical alternative is to provide a layer onto the part of a material'having the necessary hardness. This approach is also advantageous in that many very hard materials, if formed into a large part are easily broken when subjected to shock and forthat reasonare not satisfactory. Still further, very hard materials are frequently practically impossible or impractical to machine and can only be formed into complex shapes by casting,'which may be a criterion for rejection in certain cases.

It is a further usual requirement thatsuch a hard surface coating or layer be capable of resisting corrosion as well as being able to withstand relatively high heat without experiencing deterioration of its desirable properties. For example, in the case of valve seats, a satisfactory coating or cladding material must have high resistance to abrasion, heatand corrosion, the latter property being crucial where the valve may be exposed to relatively corrosive chemicals. In the past, the application of a hardened coating to a metal part has been a relatively difficult matter accomplished in certain cases by conventional welding, where the layer material composes the welding rod. In other cases, the entire metal part has been provided on the part in cast form, which necessitated the entire part being subjected to high temperature, resulting in undesirable stress patterns within the part, which can lead to breakage.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, a primary object and aim of the present invention to provide improved method and apparatus for producing a hard resistant layer onto the surface of a metal part of select geometry.

Another object is the provision of method and apparatus for providing a hard, corrosive resistant coating on a selected surface of metal parts of uniform thickness and predetermined geometry.

A still further object is the provision of method and apparatus for locating a coating material onto predetermined surface areas of a metal part, forming the coating material into an adherent layer on the part, and tinishing the layer to prescribed dimensions and surface condition, all in a continuous and automatic manner.

Yet another object is the provision of a tough, corrosion resistant cladding onto selected areas of a metal part in a simplified and inexpensive manner.

In summary, a metal part to be clad in accordance with the practice of this invention is conveyed past a plurality of treating stations arranged along a definite path. At the first station, the metal part has the surface on which the coating or cladding is to be applied machined to include a receiving groove. The part is then transported to the next station where a suitable hard cladding material in particulate form is deposited onto the specially machined area of the metal part. The part is then heated to where the temperature of the coating material is raised sufficiently to melt it, then the metal part is moved to a finishing station where the coating is machined to prescribed dimensions and surface condition.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of the preferred form of the apparatus of the present invention.

FIG. 2 isa schematic plan view of the apparatus of FIG. 1.

FIG. 3 is a perspective, plan FIG. 1.

FIG. 4 depicts in elevational, sectional view, a typical workpiece at different stages of development in accordance with the practice of the invention.

FIG. 5 is a perspective view of the finished workpiece.

FIG. 6 is an elevational, partially sectional view of the workpiece.

FIG. 7 is an elevational, partially sectional view of that part of the apparatus for applying coating material to the workpiece.

view of the apparatus of FIG. 8 is an enlarged elevational section of the apparatus of FIG. 7 depicting application of coating material to a workpiece.

FIG. 9 is an elevational depiction, partially in section, of that part of the invention for adhering the coating material to the workpiece.

DESCRIPTION OF A PREFERRED EMBODIMENT With reference now to FIGS. 1-3, the apparatus of the invention is identified generally by the reference numeral 20. A metal part of workpiece 21, mounted in any one of a plurality of holders 22, is carried along a generally circular path by conveyor means 23 through different operating stations. More particularly, the apparatus 20 includes l) a loading and unloading station 24, (2) a workpiece rough cut machining station 25, (3) coating material application and fusing station 26, and (4) a hardened coating finishing station 27. That is, the workpiece is first machined to a'suitable surface condition; a prescribed amount of powdered coating material is disposed onto the machined surface; the coating material and adjacent portions of the workpiece are then raised to an elevated temperature to fuse the coating material; and after the coating material has set up, the coating surface is finished off to final desired geometry and surface condition.

Although the present invention is not confined to treating a workpiece of any particular geometry, for purposes of description, the workpiece 21 is seen to include a generally hollow tubular body having an enlarged flange 28 at one end. The flange is to be provided on its outwardly directed surface a hardened coating. Specifically, the workpiece 21 is a valve seat, the outer flange surface of which, in use, is repeatedly subjected to-exceptionally high seating pressures and abrasive forces, which, unless hardened as in the case of the present invention, would rapidly cause the valvev to leak and require replacement of the valve seat.

With reference now simultaneously to FIGS. 4-6, the workpiece blank 21 is positioned onto a holder 22 by a chuck or retaining jaw means 29 at an angle of with respect to the vertical. Additionally, the workpiece is marked by a punch 30, the pointed end 31 of which is powered against the workpiece to identify what will be the low side of the part after rough-cut machining. Selective indexing rotation of the conveyor means 23 brings the workpiece into the machining station 25 where the upper end of the blank 21 is'machined to a horizontal condition as is illustrated in FIG. 4 as ROUGH CUT. Additionally, the flange outer surface is formed to include a continuous V-shaped groove 32 for a use and a purpose to be described.

After machining, the rough cut workpiece blank 21 is then moved into the station 26. The powdered coating material dispensing apparatus 39 is swung by support arms 40 and 41 about a pivot point 42 to a position directly above the holders 22 and selective initiation of actuation and positioning of the apparatus 39 is accomplished by a pneumatic drive 43 in a conventional manner.

The workpiece 21 now includes a supply of powdered alloy 44, as is shown and identified as POWDER DEPOSIT in FIG. 4, evenly distributed on the upper surface of the flange 28 and within groove 32. The powdered alloy deposition apparatus 39 is now swung to the non-operating position shown in FIG. 3 without further indexing the holders 22, but rather leaving the holders and workpiece in the station 26. In a way that will be more clearly described later, the alloy 44 is heated to a sufficiently high temperature that it forms a continuous molten layer on the upper surface of the flange 28.

After the alloy has cooled, setting up into a hard coating 45, the platform 23 is indexed further in a clockwise direction to bring the workpiece into station 27 where the hardened coating upper surface is machined to prescribed final dimensions and condition.

With reference now additionally to FIG. 1, it is seen that each holder 22 is rotatably mounted in the platform 23 via a shaft 47 which extends below the plateform 23 and is provided adjacent its lower end with a drive pulley 48. When a pair of holders 22 reside in station 25, the rough machining station, the associated pulleys 48 are frictionally engaged by a drive belt 49 which is driven via guide pulleys 50 by a power source 51. That is, while the holders and workpiece carried thereby are in the station 25, they are rotated in a counter-clockwise direction which assists the machining operation.

Similarly, when holders 2 2 and workpieces are dis.-

posed in the station 26, their drive pulleys are frictionally engaged by a belt 52 which is provided with rotative power by an electric motor or other suitable power source 53. In this case, rotation of the workpiece insures application of powdered alloy to the areas of the workpiece to be coated in an even and continuous manner along the groove 32. Also, rotation during the heating step provides continuous and uniform melting of the alloy creating a homogeneous molten alloy coating on the workpieceflange.

A still further holder and workpiece drive system including a drive belt 54 and power source 55 rotates the holders 22 when they are'located in the final machining station 28.

Turning now to the detailed construction of the powdered alloy metering and dispensing apparatus 39, reference should be made to both FIGS. 7 and 8. A hopper or storage container 56 includes a supply of powdered coating material 57, which can flow along a gravity path throughan opening 58 in the container bottom. An L-shaped mounting bracket 59 supports a hollow tube 60, which, at its upper end, terminates in a threaded member 61 into which the threaded lower extremity of'the hopper 56 is received. The lower end of the tube 60 passes through an opening in a stanchion 62 and has a threaded extremity which is received within a similarly threaded feed tube 63. A flexible hollow tube 64, within the tube 60, concentric therewith, extends throughout its complete length with the walls of the flexible tube being adhered to the inner wall surface of the tube 60. First and second openings 65 and 66 are formed in opposite sides of the tube 60, the opening 65 being at substantially the middle of the tube long dimension and the opening 66 displaced slightly downwardly toward the lower extremity of the tube.

A clamping head member 67, carried at the end of a rod 68 is mounted onto a crossbar 69, which in turn rides on two guidestuds 70 and 71 for motion transversely of the tube 60. A spring 72 provides head member 67 with individual limited resilient movement relative to the crossbar. A hydraulic drive cylinder and piston means 73 is actuable in one direction to move the crossbar 69 and head member 67 to the left as shown in FIG. 7, such that the head member engages the resilient tube 64, compressing its walls together, preventing flow of the powder 57 through the tube. At this same time, a second head member means 74, of identical construction to that just described, is situated in a withdrawn condition whose head member is disposed spaced from the-tube 64 and immediately opposite the opening66, Actuation of the hydraulic means 73 in the opposite direction causes the crossbar 69 and head member 67 tomove away from the flexible tube 64, while simultaneously causing the head member means 74 to engage the tube 64 and close it to the position shown in the dotted line. During each of these transfer conditions, a measured amount of powder 57 moves downwardly through the tube 64 and outwardly of the feed tube 63 to the metering and dispensing apparatus 75 to be described below.

The apparatus described in the paragraph immediately above functions to fill a secondary hopper 76 of the apparatus 75, which hopper includes a feed tube 77 extending along a gravity path with its lower end communicating with a powder feed means 78. The means 78 is hollow and includes a flexible hollow tube 79 secured therewithin, the wall'sof which are contiguous to the inner walls of the chamber as shown. A conical head 80 is threaded onto the means 78 and provides a constricted passageway via which powdered alloy is dispensed onto the workpiece upper surface. An opening 81 in the feed means wall is aligned with the bore of a guide tube 82 mounted on members 83, 84 and 85. On the side of the block 85 thereis secured a hydraulic (or pneumatic) cylinder 86, including a drive piston 87 connected to a drive rod 88 which extends through the bore of the guide tube 82. A coil spring 89 is received onto the rod 88 and interacts between the end wall 90 of the cylinder 86 and the piston 87 to urge the rod 88 toward the left as shown in FIG. 8. When hydraulic (or pneumatic) fluid is provided via the tubing 91 into the cylinder 86, the piston is driven against the spring force moving the rod 88 to the position depicted, which allows powder to move downwardly and through the metering head 80 onto the upper surface of the workpiece 21. With the fluid pressure removed, the spring moves the rod 88 against the flexible tube 79, closing it and stopping powder dispensing. Optionally, it may be advisable to provide a vibrator (not shown) for shaking the lower end of the hopper 56 and associated members to enhance feeding of the powder and prevent its clogging in the restricted passageway of the tube 64.

As best shown in FIG. 8, an adjustment locking screw 92 is threadedly received in the lower part of the member 84 and bears against the guide tube 82 for providing vertical adjustment of the positioning of the head 80 with respect to the workpiece 21.

Reference is now made to FIG. 9 and a preferred form of heating apparatus 93 for melting the powdered alloy previously deposited on the workpiece under surface. A hollow tube helical coil 94 has its tube ends anchored in a support base 95. An insulative, open-end cylinder 96 surrounds the coil 94 and is spaced there from at all points. A secondary winding or coil 97 is arranged on the outer surface of the cylinder and its ends are connected to a work coil 98 that projects beyond the edge of a mounting plate 99 which also carries the insulative cylinder 96. Passageways 100 within the plate 99 carry a coolant provided via a hose 101 to maintain the plate at a sufficiently low temperature throughout operation.

A cylinder 102 is mounted to the underside of the support base 95 and is provided with a source of hydraulic (or pneumatic) fluid by hose 103. A piston 104 included within the cylinder connects with a drive rod 105, the outer extremity of which is secured to the plate 99 as at 106. Accordingly, at the extreme left drive position as shown in FIG. 9, the work coil 98 is directly over the workpiece 21, and the coil 94 is within the cylinder 96 and coupled to the secondary coil 97. Driving the piston 104 to its rightmost position moves the work coil 98 away out of registry with the workpiece and moves the cylinder 96 away from the coil 94, thereby uncoupling the coils 94 and 97.

Electrical operation of the heating means 93 is conventional and is frequently referred to by. the term induction heating. Briefly, high-frequency electrical power applied to the coil 94 produces a voltage in the coil 97 and work coil by transformer action. When the work coil is registered with the workpiece, the highfrequency current in the work coil 98 induces eddy currents in the powdered alloy and adjacent metal parts of the workpiece which heat them.

What is claimed is:

1. Process for providing a hard metal alloy coating on restricted or confined surface portions of a metal part such as a valve seat, said process comprising in the order given the steps of:

. 6 supporting the part with the portions thereof to be 5 coated disposed substantially horizontally and facing upwardly;

machining said surface portions of the metal part to be coated to predetermined condition and to include a groove therein opening upwardly; moving the supported metal part along a definite 5 path through a plurality of treating stations;

moving a powdered hard metal alloy coating material which is in solid state along a gravity path onto the portions of the metal part to be coated in a first station; moving the metal part and powdered alloy carried thereby into operative juxtaposition with an induction heating means in a second station; applying electric power to said induction heating means while said metal part and powdered alloy are in said second station, whereby the powdered alloy is heated sufficiently to form a molten mass; moving the metal part and molten alloy coating thereon through the free air to cool and solidify the molten alloy coating; and machining the solidified hard metal alloy coating thereby shaping said coating to predetermined dimensions and condition.

2. Process for forming a hard metal alloy coating on 2 an end portion of a metal part, comprising in the order given the steps of:

mounting the metal part with the end portion to be coated disposed generally horizontally and facing upwardly;

conveying the mounted metal part along a definite path;

machining the end portion of the mounted metal part to be coated to predetermined condition and to include a groove therein of closed path geometry and opening upwardly;

rotating the metal part about a vertical axis;

depositing a powdered hard metal coating alloy which is in solid state onto the metal part end portion while it is rotating and in covering relation to the groove formed therein;

melting the powdered alloy while it rests on the metal part end portion; cooling the molten alloy until it solidifies into a hard metal coating on said metal part; and

machining the solidified hard metal coating on said metal part to predetermined condition and dimensions.

3. Apparatus for treating restricted or confined surface area portions of a metal workpiece such as a valve seat to provide a hard metal surface thereon, said apparatus comprising:

a conveyor for indexingly moving the workpiece along a definite path; machining means located along a path of movement for forming the restricted to confined surface areas of the workpiece into a predetermined configuration including a groove therein opening upwardly;

means for depositing in solid state a mass of metal powder harder than that of the workpiece onto the restricted or confined machined areas of the workpiece;

means for raising the temperature of the powdered metal mass to at least its melting point; and second machining means located in spaced relation along the definite path from the temperature raising means for shaping the hard metal mass to a predetermined configuration after it has solidified.

4. Apparatus as in claim 3, in which the temperature raising means includes an induction heating unit having an induction coil disposed immediately adjacent the workpiece and metallic mass thereon for inducing heating currents within the mass.

5. Apparatus as in claim 3, in which the means for depositing the mass of powdered metal includes a hopper for containing a supply of powdered metal alloy located above the path of movement of the workpiece, and selectively actuatable means connected to the hopper whereby, as the workpiece moves thereunder, actuation of said means provides a metered quantity of said alloy onto the select surface areas of the workpiece by gravity flow.

6. Process of providing the end portions of a generally cylindrical metal part with a hard metal alloy coating thereon, said process comprising in the order given the steps of:

supporting the metal part with the end portions to be coated maintained in a substantially horizontal upwardly facing orientation;

machining the end portions to predetermined condition and to include a groove therein opening upwardly;

indexing the metal part along a generally circular path through a plurality of treating stations while maintaining the same general orientation of the metal part throughout;

rotating said cylindrical metal part about its axis in a first station;

metering a quantity of powdered hard metal alloy in solid state along a gravity path onto the end portions of the metal part while it is rotating, thereby substantially covering said end portions with said powder;

induction heating the powdered alloy to raise the temperature thereof sufficiently to melt the alloy in a second station;

air cooling the molten alloy until it solidifies as a hard metal coating on the metal part; and

machining the solidified hard metal alloy coating to predetermined dimensions.

7. Apparatus for forming a hard metal alloy coating on a selected confined surface portion of a metal workpiece, said apparatus comprising:

a table conveyor adapted for rotative motion;

means selectively actuatable for rotatively indexing the conveyor in a first direction;

support means on the upper surface of said conveyor for removably receiving the workpiece thereon and presenting the surface portion of the workpiece to be coated in a generally upwardly facing direction;

machining means for forming the surface portion of the workpiece to a predetermined condition to include a groove therein opening upwardly;

a source of supply of powdered hard metal alloy mounted adjacent the conveyor and including conduiting means with an exit opening immediately above the path along which the conveyor moves the workpiece;

means for rotating the support and workpiece carried thereby while being conveyed adjacent the source of powdered metal alloy;

means selectively actuatable for moving the powdered alloy from the source of supply through said conduiting means and out the exit opening thereof to deposit upon the portions of the workpiece to be coated;

an induction heating coil disposed above the path of movement of said workpiece at such location that the workpiece and powdered alloy carried thereon will move immediately adjacent said coil;

means interconnecting said coil with a source of alternating voltage and selectively actuatable to induce heating currents within the powdered alloy as it moves therepast, whereby the alloy is brought to a molten condition which upon solidification provides the desired hard metal alloy coating; and

means for machining the solidified hard metal alloy coating. 

1. Process for providing a hard metal alloy coating on restricted or confined surface portions of a metal part such as a valve seat, said process comprising in the order given the steps of: supporting the part with the portions thereof to be coated disposed substantially horizontally and facing upwardly; machining said surface portions of the metal part to be coated to predetermined condition and to include a groove therein opening upwardly; moving the supported metal part along a definite path through a plurality of treating stations; moving a powdered hard metal alloy coating material which is in solid state along a gravity path onto the portions of the metal part to be coated in a first station; moving the metal part and powdered alloy carried thereby into operative juxtaposition with an induction heating means in a second station; applying electric power to said induction heating means while said metal part and powdered alloy are in said second station, whereby the powdered alloy is heated sufficiently to form a molten mass; moving the metal part and molten alloy coating thereon through the free air to cool and solidify the molten alloy coating; and machining the solidified hard metal alloy coating thereby shaping said coating to predetermined dimensions and condition.
 2. Process for forming a hard metal alloy coating on an end portion of a metal part, comprising in the order given the steps of: mounting the metal part with the end portion to be coated disposed generally horizontally and facing upwardly; conveying the mounted metal part along a definite path; machining the end portion of the mounted metal part to be coated to predetermined condition and to include a groove therein of closed path geometry and opening upwardly; rotating the metal part about a vertical axis; depositing a powdered hard metal coating alloy which is in solid state onto the metal part end portion while it is rotating and in covering relation to The groove formed therein; melting the powdered alloy while it rests on the metal part end portion; cooling the molten alloy until it solidifies into a hard metal coating on said metal part; and machining the solidified hard metal coating on said metal part to predetermined condition and dimensions.
 3. Apparatus for treating restricted or confined surface area portions of a metal workpiece such as a valve seat to provide a hard metal surface thereon, said apparatus comprising: a conveyor for indexingly moving the workpiece along a definite path; machining means located along a path of movement for forming the restricted to confined surface areas of the workpiece into a predetermined configuration including a groove therein opening upwardly; means for depositing in solid state a mass of metal powder harder than that of the workpiece onto the restricted or confined machined areas of the workpiece; means for raising the temperature of the powdered metal mass to at least its melting point; and second machining means located in spaced relation along the definite path from the temperature raising means for shaping the hard metal mass to a predetermined configuration after it has solidified.
 4. Apparatus as in claim 3, in which the temperature raising means includes an induction heating unit having an induction coil disposed immediately adjacent the workpiece and metallic mass thereon for inducing heating currents within the mass.
 5. Apparatus as in claim 3, in which the means for depositing the mass of powdered metal includes a hopper for containing a supply of powdered metal alloy located above the path of movement of the workpiece, and selectively actuatable means connected to the hopper whereby, as the workpiece moves thereunder, actuation of said means provides a metered quantity of said alloy onto the select surface areas of the workpiece by gravity flow.
 6. Process of providing the end portions of a generally cylindrical metal part with a hard metal alloy coating thereon, said process comprising in the order given the steps of: supporting the metal part with the end portions to be coated maintained in a substantially horizontal upwardly facing orientation; machining the end portions to predetermined condition and to include a groove therein opening upwardly; indexing the metal part along a generally circular path through a plurality of treating stations while maintaining the same general orientation of the metal part throughout; rotating said cylindrical metal part about its axis in a first station; metering a quantity of powdered hard metal alloy in solid state along a gravity path onto the end portions of the metal part while it is rotating, thereby substantially covering said end portions with said powder; induction heating the powdered alloy to raise the temperature thereof sufficiently to melt the alloy in a second station; air cooling the molten alloy until it solidifies as a hard metal coating on the metal part; and machining the solidified hard metal alloy coating to predetermined dimensions.
 7. Apparatus for forming a hard metal alloy coating on a selected confined surface portion of a metal workpiece, said apparatus comprising: a table conveyor adapted for rotative motion; means selectively actuatable for rotatively indexing the conveyor in a first direction; support means on the upper surface of said conveyor for removably receiving the workpiece thereon and presenting the surface portion of the workpiece to be coated in a generally upwardly facing direction; machining means for forming the surface portion of the workpiece to a predetermined condition to include a groove therein opening upwardly; a source of supply of powdered hard metal alloy mounted adjacent the conveyor and including conduiting means with an exit opening immediately above the path along which the conveyor moves the workpiece; means for rotating the support and workPiece carried thereby while being conveyed adjacent the source of powdered metal alloy; means selectively actuatable for moving the powdered alloy from the source of supply through said conduiting means and out the exit opening thereof to deposit upon the portions of the workpiece to be coated; an induction heating coil disposed above the path of movement of said workpiece at such location that the workpiece and powdered alloy carried thereon will move immediately adjacent said coil; means interconnecting said coil with a source of alternating voltage and selectively actuatable to induce heating currents within the powdered alloy as it moves therepast, whereby the alloy is brought to a molten condition which upon solidification provides the desired hard metal alloy coating; and means for machining the solidified hard metal alloy coating. 